What's eating books

Despite continual progress in data storage and increasing volume of digital sources, paper is still the most durable historical medium of data storage. Unfortunately, due to physical, chemical, and biological factors, it deteriorates easily. One of the most common symptoms of book, drawings and photographs degradation, especially those dated back to the cusp of the 20th century, is rusty brown discolouration known as paper foxing.

Diagnosis

Numerous studies around the world have been conducted to identify the mechanism of foxing. Even though the problem has been known since the 1930s, we still haven't found what causes the phenomenon. It is thought that microorganisms might be responsible for this kind of damage. According to a different theory, the rusty brown discoloration is caused by oxidation of iron compounds originating from iron elements of machines or water used in the production process.

So far, in their quest to solve the mystery of paper foxing, scientists have used many research methods (microscope analysis, chemical analysis, microbiological analysis), yet none of them has allowed them to fully explain its underlying mechanism. In recent years, omics (metagenomics, metabolomics) methods have been become particularly popular and revolutionized the way environmental studies are approached.

The method developed at Lodz University of Technology

Scientists from the TUL's Institute of Fermentation Technology and Microbiology in collaboration with the Laboratory of Bioorganic Chemistry of Rzeszów University of Technology and the Bionanopark in Łódź took advantage of the breakthrough in research techniques. They set out to discover the mystery of paper foxing on 19th century paper. New generation sequencing (NGS) - previously successfully applied to studying biodiversity of microorganisms colonizing technical materials - was used in the study as well as high-resolution surface-assisted laser desorption/ionization time-of-flight mass spectrometry imaging using the gold nanoparticle-enhanced target (AuNPET SALDI-ToF-MS). It is a novel method of mass spectra analysis and imaging of chemical compounds and complex biological mixtures. 

Results

Interestingly, both moulds as well as bacteria may be responsible for the rusty brown discolouration. On the historic paper, the team of researchers identified bacteria in the genera of Ralstonia, Bacillus, Pseudomonas, and Delftia as well as Cladonia, Phoma and Pyrenochaeta moulds. The microorganisms were typical only to those samples of the paper affected by foxing, which may be indicative of their relation to this phenomenon. Metabolomics allowed the scientists to identify chemical compounds described with the following molecular formulae C30H42O (8'-apo-beta-carotenol) and/or C27H46O2 (24-hydroxycholesterol). It is worth pointing out that these compounds may be yellowish orange just like the foxing stains.

Studies to explain the mechanism of rusty brown discolouration are not only still going on - they are picking up speed. We seem to be only a step away from solving the mystery of foxing.